Party-line telephone system



@July 12, 1960 l E. sKOGsBERG 2,945,095

PARTY-LINE TELEPHONE SYSTEM Filed March 14', 195e 5 Sheets-Sheet 1 INVENT OR El/.xcajsbezf A'I'ITORNEE July l2, 1960 E. l.. sKoGsBERG 2,945,095

PARTY-LINE TELEPHONE SYSTEM Filed March 14, 1956 5 Sheets-Sheet 2 s Pw-'HHM'- D ff il #un m5 1 `[eA/2 l .SRI I l July 12, 1960 E. L. sKoGsBERG 2,945,095

v PARTY-LINE TELEPHONE: SYSTEM Filed March 14, 1956 v s sheets-sheet s ATTORNEYS 2,945,095 Y PARTY-LINE TELEPHONSYSTM Erik Lennart Skogsberg,lDomarevagen 1S, Huddinge; Sweden Filed M31'. 1'4, 1956, Ser. N0. 571,434 Claims priority, application Sweden Apr. V'2, 1955 'Ihe invention relates to la telephone system and more particularly to a multi-party telephone system.

n An object of the invention is to provide a simple and effective system Ifor 4identifying'the calling stat-ion on a multi-station telephone system. Y Y

Another object of the invention is to generate an identilication alternating current signal by means of fa transistor-generator, which signal is of a predetermined length.

A further object of the invention is to obtain a vselective call signal for calling of a particular party station of the multi-party stations connected to a line and for Control of that correct apparatus answers the call. Y

Another object of the invention is to use a transistorgenerator Ifed from the exchange over the line, whereby a current source at each subscribers telephone may be dispensed with.

A number of specific embodiments of the invention will now Ibe described with vreference to the accompanying drawings, in which Fig. 1 illustrates one embodiment of the telephone system; Fig. 1a illustrates an alternative embodiment of a transistor oscillator usable in Pig. l; Fig. lb illustrates still another alternative embodiment of a transistor oscillator usablerin Fig. 1; Fig. 2 is a detailed illustration of a telephone station; and Fig. ,3 is a -detailed illustration of the telephone exchange usable with the station of Fig. 2.

In Fig. 1, L designates a telephone line comprising the line conductors a and b, A1 an automatic lire alarm system connected to the line, A2 a telephone station connected 4to the same line and TBZ the exchange 'equipment of the line. Although not shown, a number of re alarm systems and Itelephone stations `may be' connected to the same line. l

In the tire alarm systems connection relay set A1, is shown as including relay AR and relay FR, which 'two relays in known manner are respectively responsive to alarm and fault signals in the tire alarm system.` There are further two relays CRI and CRZ of which the purpose will be explained hereinafter. There is also shown a low vfrequency oscillator OSC, which may be ot conventional type with its output transformer TA1 and the condensers CAI and CAZ- Furthermore there is included speech equipment of a.conventional type comprising an induction coil T,"a microphone `M and a receiverl-I. The microphone is divided into two halves and its center point is connected to" earth thereby providing for speech connection with.. the exchange even when one of the line conductors is faulty, e.g. over one oi the line conductors and earth. The speech equipment is connected to the line by the switch hook when` the handset is removed.

When the automatic lire alarm system A1 gives oli an alarm or fault signal the identication works in the following way. The'relay FR is released at a fault signal and relay AR at an alarm signal thereby connecting the inductance Il :between .the line conductors q and b.

2 This -is in known manner indicated by a relay in the exchange (not shown) which relay operates another relay, R13, which reverses the polarity of the line conductors. When the polarity of the line conductors is reversed, current is yfree to ow through the 'rectifier L4 and the winding of relay CRE whichv relay operates and releases delay acting relay CRL During the 'time the relays CR1 and GRZ both are in an' -actuated position, the oscillator OSC with its output .transformer TA1 and condensers CAI and CA2 is connected to the line conductors. The oscillator obtains power over contacts on the relays AR, 'FR and CRZ, 'relay CR2 also receiving holding'current over the same contacts. The oscillator generates 'a certain frequency until the relay CRI is released. This frequency iis amplified by the amplier F1, which has built in band p'ass lilters for separation of frequencies, and operates the signal lamps in the VeX- change circuitTB-Z. In vorder to establish if an alar or a fault signal, eg. if relay AR `or FR has been released in -the-automatic alarfm system A1 one of these .Y

relays, for example FR, may start an impulsing unit (not shown) which provides for the transmission the oscillator lfrequency'inp'ulses. 'Another way is to provide the relays FR and AR with contacts that tunes the oscillator to acertain frequency lfor each of the 'relays which then -may be indicated in the exchange circuit TB2. Y Y

The telephone station A2, 'FigV l, `functions in the `'saine Way as A1, but the oseill'a'tor, which here is "shown more in detail -is a -transisttn` oscillator. The speech equipment T, which 'is substantially identical with that shown in Al, is indicated in block diagrammatic forint The oscillator obtains its power 'from the exchange equipment over the Iline conductors and a low pass-iilter DRM with the condenser CA6. InV order to block the transistor from getting to -lig'h Vol-tages a Valfistbr Si is connected irl the circuit'. The oscillator frequency -may be obtained either through an entra 'winding on the transformer TA2 or over a condenser CAS and the output transformer TA1. 'In order to operate the "oscillator only when the polarity of the' line conductors is reversed a rectifier L1 is connected in series lwith the transistor. Thus the relays CRl and CR are unnecessary in the telephone systern since relay R13 is arranged to reverse the polarity of line for only a certain time during which time the oscillator works.4 This arrangement has special value when a power supply canV not be obtained at the telephone station. Naturallythe rectifier L1. may be replaced by any other device 4sensitive of the current direction, eg, a relay device, which, uponcurrent reversal on the line branches, connects the, oscillator in such a way that it will' work 'by current from the exchange over the line during a predetermined time. The exchange equipment may either be a manually operated switchboard or auto- Inati'cally working line finders and other circuits.

vA variation of the' transistor oscillator is shown in Fig. l. In order to obtain oscillation during a certain time, the transistor characteristic requiring the emitter e and the collector 'e shalll have different potentials in relation to the base bis utilized. the condenser CAS is charged through the rectier' `L2 and resistor :'21 at norma-l polarity of the line conductors. When the polarity of the line is reversed the collector c receives the right polarity through the rectifier LS, and the emitter e receives the right polarity from the recharging condenser CAS. During this time the oscillator will workV and be identifiedI in the' exchange in the manner previously described.

4Fig. lb illustrates how two oscillators OSCI and can be connected to the line. These oscillators 'are of the same type as'has been described in Figs; l l:

With this arrangement the oscillators frequency can be obtamed in the exchange equipment even when one of the line conductors is broken since one of the oscillators 1s connected between the a-conductor and earth while the other oscillator is connected between the b-conductor and earth. These two oscillators are synchronized with .each other through the resistor r22 or any other circuit 1n a known manner. i

The oscillator arrangement in Fig. lb is shown in a more detailed version in Fig. 2 where it has been combmed with means for calling the telephone station from the exchange. This means comprises the frequency sensitive relay SR1 with its matching transformer TAS, a connecting relay SR2 and a bell Rl'. A certain number of such telephone stations may be connected to the line, but for the sake of simplicity only one is shown.

i The exchange equipment TB2 to be employed is shown 1n Fig. 3, Where LR designates aline relay set, IF the line finder (only shown as a relay for each line), and CEC the common exchange circuit.

When the handset of the telephone station is removed the hook K1 is actuated and the station is connected to the line. This operates relay CR1 in LR Fig. 3 and starts the line nder LF which connects the line Ato the common exchange circuit CEC 'and operates the relay BRl. Relay BRI breaks the connection of relay CR1 to the llne. Relay R3, in CEC, is then actuated causing relay R2 to operate. Relay R2 reverses the polarity of the line conductors whereby-the oscillators in the telephone station start. Relay R2 also operates relay R4 which connects the frequency selective amplilier.` BP to the line. The amplifier selects the frequency given off at the telephone station and actuates one of the contacts F1, F2 or F3 depending upon thefrequency. One of ther-three lamps IL11-12-13 is lighted over the relay LRl operatedby the Iline finder LF thereby identifying the calling station. This operation occurs during the delayed action of relay R which is connected by relay R4. The lamps ILll-ZB can be provided with holding means in order to remain lighted. When relay R5 .operates it releases relay R2 whereupon relay R4 is released but relay R5 remains holding itself over its own contacts. When relay R2 releases the polarity of line goes back to normal and the oscillation stops in the telephone station. When relay R4 releases the speech equipment Tin the exchange is connected to the-line. As one of the lamps IL now shows which station has called the operator of the exchange connects a certain frequency from the generator LFG through the condensers C3 and C4 to the line. This frequency of generator FG corresponds to the station which has called and operates the frequency sensitive relay SR1 in the calling station through the condensers CA13, CA14 and the matching transformer TAS.- When relay SR1 operates, the relay SR2 is connected to the line through the rectifier L3 and operates, thereby getting holding current ove-r.- its own contact and connecting the speech equipment T of the station to the line.

the relays in the exchange equipment are restored andk during the delayed action of relay BRI the current through the line conductors and the Yrelay SR2 yis Vinterrupted whereupon the speech equipmentisreleased and'dis'- connectedin the telephone station.

- If the operator `of the 'exchange' Wants to call one of the telephone stations connected to one of the linesi he depresses one of the keys P1 or P2 thereby causing lthe line nder LF to Yconnect the wanted line to the common exchange circuit CEC. At the same time the relay R51 The frequency l is operated and connects the line in question to the transformer 'IF and the ringing generator RG. A ringing current is then fed to the line conductors and earth, but as no bell in any of the telephone stations is connected to the line, no bell will ring. The operator then, while pressing one of the keys P1 or P2, connects a certain frequency, corresponding to the telephone station wanted, from the -generator LFG to the secondary winding of the transformer TF and this frequency too is induced on the line. VThis frequency, as previously described,` operates the frequency sensitive relay SRI at the desired telephone station through the condensers CA13, CA14 and the transformer TAS. The relay SRI connects the bell Rz' to the line through the condensers CA11 and CA12. The center point of the bell is connected to earth and the bell then will ring by current from the generator RG in the exchange equipment. In due time the operator releases the key P1 or P2 and the ringing will stop. When the call is answered at-the telephone station,`this answer goes through to the exchange in exactly the same way as has been described before, concerning a call from the telephone station. Naturally in this case the frequency generator LFG can be preset in some Way so that only the called telephone station is connected. lAs shown in the gures the speech equipments have their center points connected to earth so that speech connection as well as identification and calling is established even if one of the line-conductors is faulty. The lines may also be controlled by a steady current to indicate when a break has occurred on the line. -Metering devices, of which the operating in known manner can be made dependent of .the answer of the called apparatus, maybe connected over contacts on said device holding the lamps L11-L23 lighted. To avoid connection of the metering device at a call to aV partytime station, the connection of themetering device may either be made dependent of the signal sending `from the operator .to the called telephone station, or may happen in lthe conventional manner in a telephone system; i.e. at a call from the party-line station only.

What I claim is:

l. In -a telephone system, a two conductor line; a centralexchange coupled .to said line and having an electrical Y amplier land second circuit closure means for selective- A ly actuating one of said indicator means in responseto the vsignal vtransmitted thereto; a plurality of par-ty stations, each having manually operable third circuit closure means for operatively coupling said station across said line, a transistor oscillator tuned to :genera-te a particular frequency signal individual .to said station, unidirectional conductive circuit means for rendering said oscillator operable upon reversal of the initial polarity of said energized line, .subsequent to the coupling of said station thereto thereby enabling transmission of said particular frequency signal to said signal frequency amplifier means atsaid central exchange.

2. In a telephone systemfa two conductor line; a central exchange coupled'to said line and having an electrical energy sourcefor energizing said line in an initial polarity, iirst switching means actuable for reversing the ini-tial polarity of said energized line, a plurality of normally unactuated identification means, signal frequency amplitier and second switching means for selectively actuating one of said identication means in response to a signal transmitted thereto; a .plurality of individual party stations, each having manually operable third switching means for operatively coupling saidvstation to said line and for actuating said rstfswitching means, transistor oscillator means tuned to develop a particular frequency signal individual to saidV respective station, unidirectional energy conductive means for rendering said oscillator means operable upon reversal of the initial polarity of said energized line subsequent Ito the coupling of said station thereto thereby enabling transmission of said developed particular frequency signal to said signal frequency amplier means for actuation of one of said identiiication means indicative of the station coupled to said line. i

3. In a telephone system according to claim 2 wherein said transistor oscillator means comprises a pair of transistor oscillator circuits serially coupled across said line and having the common junction therebetween coupled to ground.

4. In a telephone system according to claim 2 wherein said central exchange further includes fourth switching means actuable a predetermined time after actuation of one of said identification means for deactuating said frst switching means thereby to resume .the initial polarity energization of said two conductor line.

5. In a telephone system according to claim 2 wherein said central exchange still further includes a frequency signal generator adaptable to be manually tuned to impress acnoss said two conductor line a signal having a References Cited in the le of this patent UNITED STATES PATENTS 2,164,033 Halligan i June 27, 1939 2,277,228 Hecht -..n n Mar. 24, 1942 2,387,671 Lundstrom Oct. 23, 1945 2,562,594 Bielenberg s July 31, 1951 2,581,900 Baker ...6-..- Ian. 8, 1952 2,615,094 Mitchell Oct. 21, 1952 2,717,279 Matlack et a1 Sept. 6, 1955 2,782,259 Dimond Feb. 19, 1957 

